Physio Flashcards
Fertilization occurs around day: _____ allowing for what?
Fertilization occurs around day: 15-16, allowing for recombination of genetic material to form new genetically distinct organism and intiates embryonic development.
Following ovulation, the fimbriae of the fallopian tube sweep over the ovarian surface & pick up the _________________
Following ovulation, the fimbriae of the fallopian tube sweep over the ovarian surface & pick up the cumulus-oocyte complex
Spermatozoa enter the vagina near the _____ & must reach the _____ of the oviduct where fertilization occurs
cervix
ampulla of the oviduct
Large numbers of sperm in the ejaculate generally are required for successful fertilization of the egg by one sperm. Of the ~ 300 million sperm typically ejaculated, only ____ reach the oviduct.
Clinically, males with <_______ sperm per milliliter of ejaculate are considered to be infertile
Large numbers of sperm in the ejaculate generally are required for successful fertilization of the egg by one sperm. Of the ~ 300 million sperm typically ejaculated, only 200 reach the oviduct.
Clinically, males with < 20 million sperm per milliliter of ejaculate are considered to be infertile
Sperm transport is largely dependent on the female reproductive tract &, while the sperm are still in the uterus. How does it help?
- Estrogen causes cervix to secrete WATERY mucus -> forms channels that help sperm pass through cervix, allowing only MOTILE sperm to pass
- Estrogen causes contractions of myometrium to help propel sperm
Fertlization is made up of what steps?
1. Capacitation
2. Acrosome reaction
Capacitation
Capacitation is a event that occurs in the oviduct that alters spermatizoan so it be prepared to fertlize egg.
- Oviduct fluids wash away inhibitory factors (cholesterol), located on the sperm.
- Membrane becomes permeable to Ca2+; altering movement of flagella and activating sperm
- Sperm is now activates and can release enzymes
To fertilize the egg (ovum), the sperm must penetrate through:
- Cumulus cell matrix (corona radiata)
- Zona pellucida
- Plasma membrane (oolemma)
What can occur after capacitation?
Acrosome reaction -> capacitated sperm releases ezymes from acrosome (hylauronidase and proteolytic enzymes) to break through 3 different layers of the ovum.
_________ reach the egg (surrounded by its expanded corona radiata) in the ampulla of the oviduct
capacitated sperm
Describe fertilization
- The sperm head passes the follicular cells & attaches to the zona pellucida that surrounds the oocyte, attaching to ZP3 (glycoprotein).
- Acrosomal reaction occurs: a rise in Ca2+ in the sperm will cause fusion of acrosome membrane with sperms cell plasma membrrane and exocytoze contents, which contains hydrolytic enzymes
- Hydolytic enzymes allow sperm to penetrate the zona pellucida.
- Cell membrane of sperm and occyte fuse: contents of. sperm enter cell and the. sperm cell membrane stays behind
- Increase Ca+ inside the oocyte triggers a cortical reaction: granules underneath the ovum plasma membrane undergo exocytosis, which release enzemes that harden the ZP, preventing polyspermy.
- Increase Ca2+ will also cause completion of oocytes 2nd meiotic division -> 2nd polar body (contains haploid number of unduplicated maternal chromosomes) and forms a pronucleus around female chromosomes.
- Sperm DNA decondenses -> becomes male pronucleus
- M and F pronuclei fuse -> ZYGOTE -> 1st embryonic cleavage.
What blocks polyspermy?
ZP2
What. initiates acrosome reaction?
Binding of sperms ZP3 receptor to ZP3.
Without going through capacitation, the sperm lacks what?
ZP3 receptor, thus, capacitation cannot occur
What represents the END of fertilization and BEGINING of embryonic develpoment?
Mingling of M/F chromosomes
What are the two steps of embryonic develpoment?
1. Compaction and blastocele develpoment
2. Blastocyst hatching
1st week of embryogenesis occurs where>
in the lumen of the oviduct and uterus,
Describe
- Compaction and blastocele develpoment.
- Blastocyst hatching
- 1st 2 cleaves 2 days.
- Day 3: we formed a morula (16 cells),
- 3.Desmosomes and gap junctions compacts the cells bringing them closer together
- Day 4: Early blastocyst forms inside d/t active transport of Na+ and osmosis of water.
- Outer cells of blastocyst become the trophoectoderm (trophoblast); those in the middle becoming the inner cell mass (ICM) ->
- 6-7 days after ovulation: Lytic factors from endometrium (plasmin) and the trophoblast degenerates the zona pellucida -> releasing the hatched blastocyst -> can implant on endometrium
What do the ICM and trophoectoderm become?
- ICM are pluripotent and will become “embryo proper”,
- Trophectoderm will form the placenta & extra-embryonic tissues
What happens if hatching does not occur?
infertility. bc embryo cant. grow and develop
What happens if premature hatching occyrs?
Uterine secretions do what?
- nourish the preimplantation embryo,
- promote growth, &
- prepare it for implantation
The presence & action of ________ may determine the extent of the implantation window
pinopods
Blastocyst must avoid rejection by the maternal cellular immune system in order to survive. What. are they?
- Immunosupressive/immunoregulatory. agents
- hCG prevents menstruation by sustainsing CL, telling the mom she is pregnant.
______ is one of the most important of the factors secreted by syncytiotrophoblasts, when?
hCG is one of the most important of the factors secreted by syncytiotrophoblasts, both before & after implantation.
- Related to LH -> sustains CL when LH levels fall
- Autocrine GF that promotes trophoblast growth and development of placenta.
Eventually during implantation, trophoblast differentiate into 2 cell types:
1. Cytotrophoblasts,
2. Syncytiotrophoblasts
Cytotrophoblasts actions
Supporting cells: Rapidly proliferates and provides a layer of cells that continuously divide.
Syncytiotrophoblasts
has adhesive, invasive, & endocrine functions.
Endocrine:
- secretes hCG when implantation occurs
- Makes progesterone to maintain pregnancy, independent of CL
WHAT ARE THE 3 STAGES OF IMPLANTATION?
1. Apposition
2. Adhesion
3. Invasion.
Implantation:
occurs where>
Posterior wall of uterine fundus
Implantation:
Step 1: Apposition
- Endometrium and trophoblast contact, in the crypts of the endometrium.
- Inner cell mass rotates so that it faces the endometrial epithelium
Implantation:
Step 2: Attachment
- Trophoblast attaches to the uterine epithelium via microvilli.
- Ligand receptors are probs involved; causing changes in decidual cells by. disloging from connection to basal lamine.
Implantation:
Step 3: Invasion
- Degradation of endometrial epithelial cells
- Trophoblasts fuse into endometrium and form synctiotrophoblast and cytrophoblast.
- During implantation, synctiotrophoblast send protrusions into the cells and dissociate them by. secreting TNF-a, which interferes with cadherins and B-catenin.
- Penetrate until reach stroma
- Trophoblast secrete autocrine facts (syncitiotrophoblasts. -> hCG) -> invade.
- Metalloproteases & serine proteases degrades the ECM
Decidualization -> Response of maternal cells (stromal cells) to ______.
Progesterone.
When progesterone is sensed, endometrial stroma becomes decidual cells.
Endometrium is now called decidua, making adhesive junction that inhibit implanting embryo from migratig -> ready 4 implantation.
How do we make placenta?
- Invading syncytiotrophoblasts break through endometrial veins first -> arteries later; allowing lacunae to interact with moms vessels.
- Cytrotrophoblasts. proliferate. -> create primary chorionic villus.
- PCV continue to grow.
- Mesenchymal cells from the extraembryonic mesoderm invade the 1 chorionic villi -> 2 chorionic villus
- Mesenchymal cells form fetal blood vessels de novo, villi are then known as 3 chorionic villi
Decidualization is what
response of maternal cells (stromal cells) to progesterone, causing them to to
endometrial stroma to TRANSFORM INTO glycogen filled decidual cells.
The prescence of pinopods may determine. the extent of the implantation windo.
Their development is enhanced by ________ but inhibited by ________
Ehanced by PROGESTERONE
INHIBITED by. ESTROGEN
